1. Field of the Invention.
This invention relates in general to communications systems, and in particular to a method and apparatus for zooming and reconfiguring circular beams for satellite communications.
2. Description of Related Art.
Communications satellites have become commonplace for use in many types of communications services, e.g., data transfer, voice communications, television spot beam coverage, and other data transfer applications. As such, satellites must provide signals to various geographic locations on the Earth""s surface. As such, typical satellites use customized antenna designs to provide signal coverage for a particular country or geographic area.
However, satellites typically are designed to provide a fixed satellite beam coverage for a given signal. For example, Continental United States (CONUS) beams are designed to provide communications services to the entire continental United States. Once the satellite transmission system is designed and launched, changing the beam patterns, and/or moving the beam coverage to different geographical locations, is difficult.
The need to change the beam pattern provided by the satellite has become more desirable with the advent of direct broadcast satellites that provide communications services to specific areas. As areas increase in population, or additional subscribers in a given area subscribe to the satellite communications services, e.g., DirecTV, satellite television stations, etc., the satellite must divert resources to deliver the services to the new subscribers. Without the ability to change beam patterns and coverage areas, additional satellites must be launched to provide the services to possible future subscribers, which increases the cost of delivering the services to existing customers.
Some present systems are designed with minimal flexibility in the delivery of communications services. For example, a semi-active multibeam antenna concept has been described for mobile satellite antennas. The beams are reconfigured using a Butler matrix and a semi-active beamformer network (BFN) where a limited number (3 or 7) feed elements are used for each beam and the beam is reconfigured by adjusting the phases through an active BFN. This scheme provides limited reconfigurability over a narrow bandwidth and employs complicated and expensive hardware.
Another minimally flexible system uses a symmetrical Cassegrain antenna that uses a movable feed horn, which defocuses the feed and zooms circular beams over a limited beam aspect ratio of 1:2.5. This scheme has high sidelobe gain and low beam-efficiency due to blockage by the feed horn and the subreflector of the Cassegrain system. Further, this type of system splits or bifurcates the main beam for beam aspect ratios greater than 2.5, resulting in low beam efficiency values.
It can be seen, then, that there is a need in the art for a communications system that can be reconfigured in-flight to accommodate the changing needs of uplink and downlink traffic. It can also be seen that there is a need in the art for a communications system that can be reconfigured in-flight without the need for complex systems. It can also be seen that there is a need in the art for a communications system that can be reconfigured in-flight that has high beam-efficiencies and high beam aspect ratios.
To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention discloses a method and system for reconfiguring an antenna system The system comprises a feed horn, a subreflector, a main reflector, and a connecting structure. The feed horn is pointed at an axis removed from the bisector axis of the subreflector. The distance between the feed horn and the subreflector can be changed using the connecting structure to defocus the feed horn with respect to the subreflector, wherein a size of the outgoing beam emanating from the main reflector changes when the distance between the feed horn and the subreflector is changed.
The method comprises selecting a geometry and a feed horn size for a desired zoomable range of an outgoing antenna beam, pointing an axis of a feed horn at a subreflector, wherein the axis of the feed horn is aligned differently from the bisector axis of the subreflector, selectively changing the distance between the feed horn and the subreflector to defocus the feed horn with respect to the subreflector, wherein a size of the outgoing beam emanating from a main reflector changes when the distance between the feed horn and the subreflector is changed, and selecting an angle for a reflector gimbal mechanism based on a desired geographic location of the outgoing beam and a desired size of the outgoing bear
The present invention provides a communications system that can be reconfigured in-flight to accommodate the changing needs of uplink and downlink traffic. The present invention also provides a communications system that can be reconfigured in-flight without the need for complex systems. The present invention also provides a communications system that can be reconfigured in-flight and has high beam-efficiencies and high beam aspect ratios.